Orientation in Gulls: effect of distance, direction of release, and wind

TitleOrientation in Gulls: effect of distance, direction of release, and wind
Publication TypeJournal Article
Year of Publication1970
AuthorsSouthern WEdward
JournalLiving Bird

During the summers of 1963 and 1964, a total of 373 adult and subadult Ring-billed and Herring Gulls (Larus delawarensis and L. argentatus) were used in homing trials. The distances of release sites from the colony near Rogers City, Michigan, ranged from 2 to 150 miles. An increase in distance of release sites from home did not have a drastic effect on success rates. Particular areas, perhaps those most likely to be familiar to birds from this colony, had especially low return rates. Return speeds were usually slow, the fastest averaging 19 miles per hour. Postponed departure from release sites and meandering homeward routes were partially responsible for slow returns. The time or hour of release had no effect, adverse or otherwise, on the homing rates. Gulls released at night usually postponed extensive flights until daylight. In the homing experiments for 319 gulls released at nine different compass directions from the colony, the Ring-bills released west-northwest of the colony had the lowest average success rate, 44%; and those released north of the colony the second lowest, 59%. In both instances, the most distant releases were adjacent to Lake Michigan or Lake Superior, both of which seemed to provide false topographical clues. The lowest Herring Gull success rate, 33% was for the southwest group. Generally, there was no single direction from which gulls seemed to experience extreme difficulty in orientation. Topographical features near release sites were more likely to cause adverse effects. There is a possibility that winds, associated with atmospheric conditions, influenced departures. The gulls departed more readily if conditions were especially suitable for flight. The "worst air conditions" were associated with completely overcast skies. Departure directions selected by gulls experiencing winds, 2 to 30 mph, from four of the eight plotted directions showed homeward preferences that were statistically significant; during periods of no wind, the birds scattered at random. High standard deviations are associated with each set of data.